Traditional bone joining implants, plates and related components for bone fixation are typically designed and manufactured from metals, polymers, allogenic, allograft or other materials that are integrally formed from a single piece of stock material. The size and shape of the bone joining implants are typically designed based on biomechanical characteristics of the bone that is being repaired by sizing the bone joining implant and fastening the bone joining implant to the bone with an appropriately sized device.
Some bone joining implants are designed with multiple components such as plates with screws or intramedullary nails with locking screws or other locking mechanisms. The bone joining implants may include multiple components in order to allow alignment of fracture fragments and/or alignment of adjacent bones. However, major components of the bone joining implants, such as a plate, nails or screws are designed and manufactured from a single piece of stock material, which allows limited control of mechanical properties of the subsequent bone joining implant and related components. It is thus desirable to construct bone joining implants and components that have material properties as close as possible to the biomechanical properties of the bone that is being repaired.
Wolff's law states that bone in a healthy person or animal adapts to loads that it is placed under. Accordingly, bone is grown in an area of high load and is resorbed or remodeled in areas of low load. When repairing fractures or joining bones, a bone joining implant that is too stiff creates a risk of bone resorption as excessive load is transferred to the bone joining implant and away from the bone. Bone joining implants that have low stiffness may result in an inability of the fracture to heal due to excessive movement at the fracture or implant breakage.
Important biomechanical aspects for internal fixation with bone joining implants include solid primary fixation to boney structure and sophisticated biomechanical behavior for fracture healing. For example, it may be desirable for the bone joining implant to be stiff and strong where it is joined or screwed into the bone but to have more flexible or elastic properties in a section that spans a fracture so as to more closely mimic properties of the bone and to permit load to be carried through the rejoined fracture sight.
Typically, primary fixation is achieved utilizing pins, screws, nails, porous surfaces, spikes or riveted fixation mechanisms. Plates and nails of joining implants act as internal fixation and alignment mechanisms for fracture segments. By designing the bone joining implant to vary materials, cross-sections, openings and other features, the implant may provide specific stiffness and stability to the fracture.
It would be desirable to manufacture a composite bone joining implant with material combinations in the same component of the implant. The value of such implants would be enhanced if they were complementary to the biomechanical features of the bone being joined or the joint being secured.